1. Field of the Invention
The present invention relates to methods of manufacturing a sealed body and a light-emitting device that can be protected from impurities from the outside.
2. Description of the Related Art
Frit glass sealing is known as a technique of sealing a space formed by two bonded glass substrates. A sealed body using frit glass sealing has high airtightness, and is applied to an organic electroluminescence (hereinafter referred to as EL) display device, a liquid crystal display device, a plasma display device, and the like.
Frit glass sealing is used particularly in an organic EL display device so that reliability of an organic EL element is improved. This is because reliability of the organic EL element is rapidly reduced when an organic EL layer and electrodes between which the organic EL layer is interposed are exposed to moisture or oxygen. As a sealing technique using frit glass for preventing exposure of an organic EL layer and electrodes to the air, for example, the technique described in Patent Document 1 is known.
In the technique described in Patent Document 1, a frit glass paste is scanned along an edge of a glass substrate while being discharged from a nozzle, whereby a partition is formed into a closed curve line of the frit glass paste. After that, baking is performed so that the frit glass paste is fused to be a frit glass. Further, the frit glass is pressed against the other glass substrate, and the frit glass is heated and melted by laser light irradiation; thus, the frit glass is welded to the other glass substrate. In such a manner, a highly airtight sealed body is formed.
However, in some cases, a frit glass sealed body has a region in which a crack is easily generated when conditions of laser light irradiation (e.g., irradiation intensity and scanning speed of laser light) are not adjusted, which results in low airtightness. For example, in an overlap region where laser light irradiation is started and ended, a crack is easily generated when the region is irradiated with the same laser light power as scanned regions other than the overlap region. The reason of this is as follows: the amount of heat applied to the overlap region is larger than that to the scanned regions other than the overlap region, and the frit glass and the glass substrate in the overlap region are thermally expanded in comparison with those in the scanned regions other than the overlap region. As a countermeasure against this, conditions such as irradiation intensity and scanning speed of laser light in the overlap region are controlled in a complex manner (Patent Document 2).